title: Inhibitory effect of somatostatin on the mechanosensitivity of articular afferents in normal and inflamed knee joints of the rat.
abstract: The effect of somatostatin on the sensory activity of primary afferents was studied in normal and acutely inflamed rat knee joints. Fine afferent nerve fibers with conduction velocities of 0.9-18.0 m/s were recorded as single units. All nerve fibers tested responded to local mechanical stimulation, movements of the joint and i.a. injections of KCl (10(-4) mol, 0.1 ml) close to the joint. Somatostatin (10(-4) mol, 0.2 ml) caused no direct response of the units. In normal joints, somatostatin did not change the discharges evoked by non-noxious movements but decreased the responses to noxious movements significantly to about 63% of the responses before the application. In acutely inflamed joints, somatostatin reduced the discharges of non-noxious and of noxious movements to about 55% and 52%, respectively. Injections of somatostatin with lower concentrations (10(-6) mol, 10(-8) mol) i.a. close to inflamed joints revealed shorter and less pronounced reductions of the responses to noxious movements. In a proportion of afferents, substance P (10(-4) mol) and bradykinin (10(-4) mol) were able to increase these responses again. These data indicate that the mechanosensitivity of articular afferents in normal joints may also be regulated by several neuropeptides based on a balance of pro-inflammatory peptides such as substance P, and anti-inflammatory peptides such as somatostatin. In an inflamed joint, pro-inflammatory peptides seem to predominate resulting in a sensitization of the peripheral nerve fibers. In this case, an application of somatostatin or its analogues could be used clinically to compensate this effect.
authors.affiliation: Physiologisches Institut, Universität Würzburg, Röntgenring 9, D-97070 Würzburg, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Heppelmann
authors.forename: Matthias
authors.initials: M
authors.lastname: Pawlak
mesh_terms: D000344:Afferent Pathways / Q000187:drug effects; D000818:Animals; D001168:Arthritis / Q000139:chemically induced / Q000188:drug therapy*; D001920:Bradykinin / Q000627:therapeutic use; D007719:Knee Joint / Q000294:innervation*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D013004:Somatostatin / Q000494:pharmacology*; D013314:Stress, Mechanical; D013373:Substance P / Q000627:therapeutic use
chemical_list: D013373:Substance P; D013004:Somatostatin; D001920:Bradykinin